Certain liquid pharmaceutical spray compositions, such as inhalation sprays, are packaged in and dispensed from non-pressurized containers equipped with a manually actuated pump and an atomizer nozzle. The pump is designed to expel with each actuation thereof a given quantity of atomized liquid from the nozzle. However, the particle size spectrum of the spray issuing from the nozzle is affected by variations in the manual force with which the pump is actuated, especially in the case of spray devices which finely atomize the liquid composition. Since the efficacy of many drugs adapted for spray application depends upon the particle size spectum of the spray, it is of utmost importance that the particle size spectrum of the spray be substantially the same with each actuation of the pump.